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The device is basically an iPhone 4, marked as having XXGB of memory on the back. It has 64 GB of memory, and some details (model number XXXXX, for example) are quite similar to the iPhone 4 prototype obtained by Gizmodo in April 2010.
The upcoming iPhone 5, which will probably be revealed in June, is rumored to have a bigger screen and a better camera. This leaked device, however, reveals very little detail about the next generation of the device, other than the notion that Apple is at least considering an iPhone with 64 GB of memory.